The present invention relates to a digital keystone modulation circuit, and especially to a digital keystone modulated circuit for transforming a digital image into a digital projection image.
A conventional optical projector is gradually replaced with a electronic projector. By scanning the original object, the electronic projector can generate a digital image and project it on a display directly. The operating process of the conventional electronic projector are shown in FIG. 1. At first, an analog signal is generated after scanning an object (step S11). Then, the analog signal is transformed into a digital image signal through an analog-to-digital transformation (step S12) and the digital image signal is stored in a memory (step S13). Finally, through a digital-to-analog transformation, the digital image signal is converted to a projection image signal projected on the display (step S14).
However, the projection image on the display usually is deformed as shown in FIG. 2. Because the traveling length of light at the top and bottom of the display is changed with the projection angle xcex8, the projection image is deformed and has a shape of a trapezoid. This is usually called a keystone deformation. FIG. 2 shows a normal projection image without the keystone deformation and the shape constructed by the four points A, B, C, D is a rectangle. If the projection angle xcex8 is an elevation angle, as shown in FIG. 2(b), the distance between the points B1 and C1 is extended and the distance between the points A1 and D1 is shortened. If the projection angle xcex8 is a dip angle, as shown in FIG. 2(c), the distance between the points B1 and C1 is decreased and the distance between the points of A1 and D1 is increased.
Although the keystone deformation can be solved by adding a set of optical lens in the projection image output unit to change the refracting angle of light, adding these optical lens will greatly increase the cost of the electronic projector. In addition, the optical lens will enlarge the size of the electronic projector which does not meet the current requirement of small size. It is therefore attempted by the applicant to provide a low-cost and effective electronic projector to deal with the keystone deformation encountered with the prior art.
An object of the present invention is to provide a digital keystone modulation circuit to modulate the keystone deformation in an electronic projector when a digital image is transformed into a digital projection image.
The digital image and the digital projection image is formed by n horizontal image signals and n horizontal projection image signals respectively wherein n is a positive integer. The digital keystone modulation circuit of the present invention includes an output controller, an output image selector, a first counting controller, a second counting controller, and a projection image frequency generator. The output controller is used for outputting a (3kxe2x88x921)th image signal and a (3kxe2x88x922)th or a (3k)th image signal in response to a first and a second state of an output image selected signal respectively. The (3kxe2x88x922)th, the (3kxe2x88x921)th, and the (3k)th image signals make up a kth horizontal projection image signal wherein k is a positive integer, 1xe2x89xa6kxe2x89xa6n, and the (3kxe2x88x921)th image signal is a kth horizontal image signal. The output image selector is electrically connected to the output controller for outputting a first counting signal in an enable state and the output image selected signal in the second state in response to a horizontal localization sync-signal from a microprocessor. The first counting controller is electrically connected to the microprocessor and the output image selector for counting in response to the first counting signal in the enable state, a kth horizontal projection image frequency, and a dot number of the (3kxe2x88x922)th or (3k)th image signal from the microprocessor, and outputting a first transforming signal to transform the first counting signal into a disable state and the output image selected signal into the first state after a first counting time. The second counting controller is electrically connected to the microprocessor and the output image selector for counting numbers in response to the output image selected signal in the first state, the kth horizontal projection image frequency, and a dot number of the (3kxe2x88x921)th image signal, and outputting a second transforming signal to transform the output image selected signal into the second state after a second counting time. The projection image frequency generator electrically connected to the microprocessor, the first counting controller, and the second counting controller for outputting the kth horizontal projection image frequency in response to a horizontal sync-signal and a sum of the dot numbers of the (3kxe2x88x922)th, (3kxe2x88x921)th, and (3k)th image signals from the microprocessor.
According to the present invention, the keystone modulation circuit further includes a memory and a modulated signal generator electrically connected to the output controller. The microprocessor and the memory can be set in the electronic projector, and the modulated signal generator is preferably a grounded port. Therefore, the digital image can be stored in the memory.
In accordance with the present invention, the (3kxe2x88x922)th and the (3k)th image signal are black image signals and the output controller comprises a multiplexer. The multiplexer is preferably a 2-to-1 multiplexer having a multiplex output control port to input the output image selected signal. The first state and the second state of the output image selected signal are a low voltage level or a high voltage level.
According to the present invention, the output image selector includes a first flip-flop, a second flip-flop, and a transforming signal output controller. The first flip-flop is electrically connected to the microprocessor and the first counting controller for outputting the first counting signal in the enable state to the first counting controller in response to the horizontal localization sync-signal and transforming the first counting signal in the enable state into the disable state in response to the first transforming signal. The second flip-flop is electrically connected to the microprocessor, the second counting controller, and the output controller for outputting the output image selected signal in the second state to the second counting controller in response to horizontal localization sync-signal and to the output controller to control the output of the (3kxe2x88x922)th or (3k)th image signal. The transforming signal output controller is electrically connected to the first counting controller, the second counting controller, and the second flip-flop for logically controlling the outputs of the first transforming signal and the second transforming signal to control the transformation of states of the output image selected signal.
Preferably, the first flip-flop includes a pre-set port for inputting the horizontal localization sync-signal, a data input port for being grounded, a clock port for inputting the first transforming signal, and an inverting output port for outputting the first counting signal. The second flip-flop includes a pre-set port for inputting the horizontal localization sync-signal, a data input port electrically connected to an inverting output port, a clock port for inputting the first or the second transforming signal, and an output port for outputting the output image selected signal. The transforming signal output controller is an assembling logic generator, preferably an OR gate.
Preferably, the first counting controller is a first counter and the first counter is a down-counter. The first counter includes a data input port for inputting the dot number of the (3kxe2x88x922)th or (3k)th image signal, a clock port for inputting the kth horizontal projection image frequency, an enable port for inputting the first counting signal, and an output port for outputting the first transforming signal.
Preferably, the second counting controller is a second counter and the second counter is preferably a down-counter. The second counter includes a data input port for inputting the dot number of the (3kxe2x88x921)th image signal, a clock port for inputting the kth horizontal projection image frequency, an enable port for inputting the output image selected signal, and an output port for outputting the second transforming signal.
In accordance with the present invention, the first counting time is the dot number of the (3kxe2x88x922)th or (3k)th image signal divided by the kth horizontal projection image frequency. The second counting time is the dot number of the (3kxe2x88x921)th image signal divided by the kth horizontal projection image frequency.
Preferably, the enable state and the disable state of the first counting signal are a low voltage level or a high voltage level. The first and second transforming signals are a positive pulse and a negative pulse respectively or a negative pulse and a positive pulse respectively.
In accordance with the present invention, the projection image frequency generator includes a phase-locked loop generator and a frequency divider. The phase-locked loop generator is electrically connected to the microprocessor, the first counting controller, and the second counting controller for outputting the kth horizontal projection image frequency to the first and the second counting controllers in response to a divided frequency. The frequency divider is electrically connected to the microprocessor and the phase-locked loop generator for inputting the divided frequency to the phase-locked loop generator in response to the horizontal sync-signal from the microprocessor, the sum of the dot numbers of the (3kxe2x88x922)th, (3kxe2x88x921)th, and (3k)th image signals, and the kth horizontal projection image frequency.
Preferably, the frequency divider is a third counter and the third counter is a down-counter. The third counter includes a load port for inputting the horizontal sync-signal, a data input port for inputting the sum of the dot numbers of the (3kxe2x88x922)th, 3kxe2x88x921)th, (3k)th image signals, a clock port for inputting the kth horizontal projection image frequency, an enable port for inputting an enable signal, and an output port for outputting the divided frequency.
According to the present invention, the dot numbers of the (3kxe2x88x922)th and the (3k)th image signals are changed with a projection angle xcex8 and a number n of the horizontal image signal. Both of the dot numbers of the (3kxe2x88x922)th and (3k)th image signals are (nxe2x88x92k+1)xc3x97tan xcex8.
In accordance with the present invention, the digital keystone modulation circuit further includes an initial image modulated dot number storage and an image dot decreasing coefficient storage. The initial image modulated dot number storage is electrically connected to the microprocessor and the first counting controller for outputting the dot number of the (3kxe2x88x921)th or (3k)th image signal to the first counting controller in response to an initial image modulated dot number from the microprocessor wherein the initial image modulated dot number storage gradually decreases one image dot in response to an image dot decreasing signal. The image dot decreasing coefficient storage is electrically connected to the microprocessor and the initial image modulated dot number storage for counting according to the horizontal sync-signal and an image dot decreasing coefficient from the microprocessor and outputting the image dot decreasing signal after the counting is finished.
Preferably, the initial image modulated dot number storage is a fourth counter and the fourth counter is a down-counter. The fourth counter includes a data input port for inputting the initial image modulated dot number to the first counting controller and a clock port for inputting the image dot decreasing signal.
Preferably, the image dot decreasing coefficient storage is a fifth counter and the fifth counter is a down-counter. The fifth counter includes a data input port for inputting the image dot decreasing coefficient, a clock port for inputting the horizontal sync-signal, and an output port for outputting the image dot decreasing signal to the initial image modulated dot number storage.
According to the present invention, the image dot decreasing signal is a positive or a negative pulse. The initial image modulated dot number is a dot number of a first or a third image signal and is changed with the projection angle xcex8 and the number n of the horizontal image signal. The dot numbers of the first and the third image signals both are nxc3x97tan xcex8. The image dot decreasing coefficient is an integer value of tan xcex8.
In accordance with the present invention, the digital keystone modulation circuit further includes a first data buffer for temporarily storing the initial image modulated dot number, a second data buffer for temporarily storing the image dot decreasing coefficient, and a third data buffer for temporarily storing the sum of the dot numbers of the (3kxe2x88x921)th, (3kxe2x88x921)th, and (3k)th image signals.